If your truck is stock then you probably don't. The rear diff. locker is a feature available on 2005+ tacomas and usually comes with ones with the Off road Package. The locker is intended to help you out if your in some mud or sand by giving both rear tires power opposed to the usual 1. You can add one to your 200 Prerunner but your gonna have to buy the rear diff kit and install a switch in your dash to get the same effect.